Polyurethane foams are widely known and used in automotive, housing and other industries. Foam is generally referred to as rigid, microcellular, or flexible. Typically, in the preparation of polyurethane foams, a tertiary amine catalyst is used to accelerate the reaction of the polyisocyanate with water to generate carbon dioxide as a blowing agent and to accelerate the reaction with polyols to promote gelling. Tertiary amines generally are malodorous and offensive, and many have high volatility due to low molecular weight. Release of tertiary amine during foam processing may present significant safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
Amine catalysts which contain primary and/or secondary hydroxyl functionality typically have limited volatility and low odor when compared to related structures which lack this functionality. Furthermore, catalysts which contain hydroxyl functionality chemically bond into the urethane during the reaction and are not released from the finished product. Catalyst structures which embody this concept are typically of low to moderate activity and are designed to promote primarily the blowing (water-isocyanate) reaction.
U.S. Pat. No. 4,957,944 discloses certain dimethylamino alkyleneoxy isopropanols for use as a catalyst for preparing polyurethane foam.
U.S. Pat. No. 5,071,809 discloses tertiary amine catalysts containing secondary alcohol functionality for use in preparing polyurethane foams. The tertiary amines containing secondary alcohol functionality are prepared by reacting an olefinic nitrile with an aliphatic polyol having at least one secondary hydroxyl functionality, followed by reductive alkylation of the resulting cyanoalkxlated polyol with a secondary aliphatic or cycloaliphatic amine, including those containing hetero atoms.
U.S. Pat. No. 4,590,223 discloses the preparation of tertiary amines containing secondary alcohols by reacting N-alkyl-piperazines with an alkyleneoxide.
Secondary alcohol functionality is preferred in these structures because the catalysts exhibit a desirable balance between their promotion of the water-isocyanate reaction and their own reactivity with isocyanates. In contrast, catalysts which contain primary alcohols react rapidly with isocyanates and thus high use levels are required. Catalysts which contain tertiary alcohols react slowly with isocyanates, but the urethanes which are formed from the tertiary alcohols have poor thermal stability. See G. Oertel, ed. "Polyurethane Handbook," Hanser Publishers, Munich, 1985, pp. 82, 84 and H. J. Fabris, "Advances in Urethane Science and Technology," Vol. 6, Technomic Publishing Co., Westport, CT, 1978, pp. 173-179. These urethanes may degrade and release the catalysts at temperatures substantially below the decomposition temperature of the foam itself. The free amine could then accelerate foam decomposition.
A catalyst which strongly promotes the polyol-isocyanate (gelling) reaction is necessary for the manufacture of many polyurethane foams. Triethylenediamine (1,4-diazabicyclo [2.2.2.]octane) is widely used for this purpose. Quinuolidine (1-azabicyclo[2.2.2.]octane) can also be used as a gelling catalyst, particularly when the polyol contains a preponderance of secondary hydroxyl groups (U.S. Pat. No. 3,036,021). Quinuclidine is more reactive than triethylenediamine for the production of polyurethane foams. Both triethylenediamine and quinuclidine are volatile materials which will not remain trapped in the foam.
U.S. Pat. No. 3,036,021 also discloses that 1-azabicyclooctanes and their alkyl, amino, hydroxyl, nitro, alkoxy and halogen derivatives can also be used as gelling catalysts, although no distinctions were made with regard to the effect of catalyst structure on activity or suitability for incorporation into a foam.
U.S. Pat. No. 4,186,040 discloses a solid, pyrotechnic composition for dissemination of 3-quinuclidinyl benzylete, the composition consisting essentially of 3-quinuclidinyl benzylete and an oxidizer incorporated in a solid foamed polyurethane binder. No information is provided on the utility of quinuclidinyl benzylete as a catalyst or as a TEDA replacement. Furthermore, quinuclidinyl benzylete does not remain trapped in the foam.